Cavity resonator device for ultra-short waves



F. coETERlE 2,496,378

CVITY RESONATOR DEVICE FOR ULTRA-SHORT WAVES Feb. 7, 1950 Filed April24, 1946 FZZEERIK COEJERIER.

INVENToR.

ATTORNEY.

Patented Feb. 7, 1950 ULTRA- SHORT WAVES Frederik Coeterier, Eindhoven,Netherlands, as-

signor, by mesne assignments, to Hartford National Bank and TrustCompany, Hartford,

Conn., as trustee Application April 24, 1946, Serial No. 664,498 In theNetherlands une 27, 1942 section 1, Public Law 69o, August 8,1946 Patentexpires June 27, 1962 12 claims. (ci. 315-6) This invention relates to aresonator, particularly a cavity resonator, and a device comprisingvsuch a cavity resonator.

The term cavity resonator is to be understood here and hereinafter tomean an oscillatory circuit for ultra-short waves constituted as acavity resonator in which a concentrated inductance and capacity aremissing and the dimensions of which are hence of the order of magnitude.of the wavelength of the fundamental frequency (smallest naturalfrequency). As set out more fully for example in Philips TechnischTijdschrift, July 1941, pages 222, 223 the said reso--V nators are amongthe non-quasi-stationary sys ems. Y

The wall of a cavity resonator constitutes a body closed on all sidesexcept, asis well-known, for the apertures which have to be formed inthe wall, for example for the wired electrical connection to the insideof the wall or for the introduc. tion of coupling loops. v-

In addition, devices for ultra-short waves are known in which use ismade of a discharge tube which is provided with means for the generationof an electron beam and in which the electron beam passes through thebore of a cavityl constructed as a cavity resonator.

The apertures formed in the wall of the reso,r nator, particularly iftheir dimensions are no longer small compared with the Wavelength, bringabout considerable lowering of the quality of the cavity resonator.

The invention has for its object to provide means for limiting this lossin quality while conserving the accessibility of the aperture with acavity resonator.

According to the invention,for this purpose the path followed by a losscurrent emerging over the edge of the aperture has connected in seriestherewith a. secondary cavity resonator provided with a. bore andpreferably constructed as a cavity resonator which has a naturalfrequency that corresponds with a natural frequency of the pri. maryresonator and which is so arranged that the aperture is in line with thebore. l

The measure according to theinventionhas the eil'ect of introducing ahigh resistance, that is the resonance resistance of'the 4secondaryresonator, into the loss current path, with the result that the losscurrent is limited.

In order that the invention may be clearly understood and readilycarried into eiect it will now be described more fully with reference tothe accompanying drawing, in which Fig. 1 is a known cavity resonator.

Fig. 2 shows a cavity resonator according to the invention having il-atsecondary cavity resonator.

Fig. 3 shows a cavity resonator according to the invention comprisingsecondary cavity resonators each of which is constituted by two conisrotation-symmetrical with respect to the axis 2 vhas apertures 4, 4'formed in its .wall 3. On excitation of the cavity resonator for exampleby means of a loop-like conductor 5, the edge of the' aperture 4, whichedge is located in a potential antinode, will be at a high-frequencyvoltage relatively to the surroundings. Due to this, other parts of theexternal surface of the cavity resonator will also be at high-frequencyvoltage relatively to the surroundings and, since the outer wall, asdenoted in the figure by l and 1', must be regarded as earthed bycapacitative agency, a considerable loss current ensues. This losscurrent, which emerges over the edge 6 of the aperture, followsthe pathshown in dotted lines in the ngure and is responsible for considerablelowering in quality of the cavity resonator.

According to the invention, this loss of quality is limited by the useof secondary cavity resonators, 8, 8' arranged in the manner shown inFig. 2 so that the said loss current is con ducted via one of thesesecondary resonators. The latter are bored at 4, 9 and 4', 9' so thatthe apertures 4 and 4' of the primary cavity resonator continueaccessible. The resonance resistance occurring between the ends 4 and 9of the secondary cavity resonator 8 is thus inserted in the losscurrent. In the case of lossfree construction of the cavity resonator 8this introduces substantial suppression of the loss current since due tothe potential distribution now occurring in the loss current path theedges l0 and l0' of the secondary cavity resonators 8 and 8 respectivelyand thus the outside of all cavity resonators will be substantially atearth potential and hence the capacity (l, 1') will have no longer anyharmful eect as regards the surrounding.

If, as hitherto taken for granted, the primary cavity resonator is notexcited in its fundamental frequency but in one of the higher naturalfrequencies, the secondary cavity resonators must obviously be tuned tothis higher natural frequency. According to circumstances, it may beadvantageous to cause the fundamental frequency of the secondary cavityresonator to correspond nally with with a higher natural frequency ofthe primary cavity resonator since the required space is thus limited.For the purpose of limiting the accuracy requirements as to thedimensions cf the cavity resonators from a mechanical point of view 1and also for compensating circuit capacities or l the like it isdesirable that use should be made of means for adjusting the naturalfrequencies of the secondary cavity resonators, for example a memberformed of insulating-material or a conductor may for this purpose'bearrangedl in the` cavity resonator concerned.

In the form of construction vshown inFig. 2A radiation losses occurthrough the apertures 9, 9' of the secondary cavity resonators S, 8 asorigiapertures 4, 4. reduced by constituting the secondary cavityresonators, as shown in Fig. -3, by two concentric hollow com'iuctorslII, ,I2 and II', I2 respectively united at corresponding, ends, theinternal condctors I2, I2' comprising'an interruption I3, I3 immediatelyadjacent the apertures 4, 4.

` lIf desired, adjoining cavity resonators may in this case have acommon wall part, as in Fig. 2. The invention may be used withparticularladvantage with devioesfor ultra-short wavesf` in which use ismade ofA la discharge tube comprising means for generating an electronbeam and the electron beam traverses the bore oi a cavity resonator,yeither for vthe/purpose of modulatingv the speed ofthe electron beainorto derive energy from the intensitymodulated beam. In such devices itis' often desirable or even necessary that the bore of the cavityresonator should be made comparativelyl large, it being so large thatparticularly with veryshortwaves the dimensions of the apertures. madein the cavity resonator are no longer, small compared with the operatingwavelength, this e'ntailing great losses.

Fig. 4 shows such a device for generating ultrashort waves towhich theinvention is applied;

A discharge tube I4 has arranged in it on the one side an electrodesystem I5 for generating the electron beam4 and on the other a collectorelectrode I6.

In between are arranged two mutually coupled primary cavity resonatorsi1 and IB respectively. The cavity resonator I'I serves for the velocitymodulation of the electron beam. In the space intermediate the twocavity resonators this velocity modulation is converted into anintensity -modulation so that the cavity resonator I8 permits'ofderivingenergy from the beam.

j For the purpose of improving the quality of the primary cavityresonators I1 and I8 provision is made of secondary cavity resonatorsI9, I9' and 20, serving solely for this purpose and conlstitutedessentially, by two concentric, hollow conductors Whose interruptedinternal conductors are aligned with the bores of the primary cavityresonators so that the electron beam can pass without any obstruction.If desired, the secondary cavity resonator maybe arranged, asdistinguished from the embodiment illustrated, entirely'outside thesurrounding envelope of the discharge tube.

In'thisconstruction, the cavity resonators I1 and I9 are not arranged indirect contact with each other but ata small distance and areinterconnected by a metal tube piece 2I in order that it ,may bepossiblefor a concentration coil 22 to be arrangedin the spaceA thus obtainedbetween the said cavity resonators.

In' the embodiments shown the primary cavity the cavity resonator Ithrough the The said radiation losses can be consequently does notconstitute a bore or else one or more apertures not arranged at the areaof apotential'antinode and also in ,the case of the primary cavityresonator having lfor example a4 concentrated capacity.

Lastly, the secondary cavity resonator may have a.,concentratedAcapacity and/or induotance in orderto'limitcthe. required space in sofar as is permittedby the quality improvement aimed at oftheprimaryhollow space resonator.

It is to be understood that the invention is not limited'to.those'specific embodiments herein described, but that variousmodifications will occur to vthose skilled in the art without departingfrom the spirit and the scope-of the invention.

l. Al cavity resonator system comprising a rst cavity resonator and asecond 'cavity resonatorhaving a resonant frequency coi-responding tothev resonant frequency of said firstv resonator"I saidv resonatorshaving contiguous wall portions pro'- vided withcoincident aperturesjthediameter of said apertures being less than fthe' Aaxial dimension ofsaid-iirst cavity resonator',ahd'said second resonator beingA` providedin lanotherwall'portion thereof with-a; second-'aperture vinline withsaid rstapertures. if "f 2.' A cavity resonator system comprisinga pri*-mary cavityresonator-havinglawall portion provided with -anaperturewliose Vdiameter isless than the axial dimension of said primaryreso'- nator, and4 means -t'o` reduce electrical 'losses oc-I curring atsaidaperture, 'svaidrnans comprising; a secondary-cavity' resonator4having a resonant frequency corresponding 'to theres'onant frequency ofsaidprima-ry resonatorfawall portion contiguous to said firstwall'portion a'nd provided with an aperture coincident with saidaperture of said first lwall portionjand-"a" second walt-pori tionprovided with'an aperture 'in 1lin'e with the apertures in saidVcontiguous wall portions. f

3. A cavity resonatorsysterncoinprising apr'ii'- mary cavityresonator-having a wall portion' provided with'an aperture whose`dian'leter is smaller than the axial dimension of said-"primary'reso-Inator, and means to reduce' electrical losses occurring at'saidaperture,v said meansfcomprising a secondary cavity resonator having aresonant frequency corresponding to the v 'resonant frequencyof saidprimary resonator, a wall portion includingsaidaperture in common withvsaid fpri'# mary resonator, and asecond wall `portion pro` rtriuded withVan aperture in linewitli said iirst'aper- 4. A cavity resonator system`comprising a primarycavity resonator havingspaced wall por tions eachprovided with an aperture, whose' diameter is small with respect to thespacing between -said wallv portions; and means'to reduce:- electricallosses occurring at said. apertures, 'said' means comprisin'garstisecondary cavity reso? nator: having awall portion contiguous toone. of 'said wall' portions` of said'primary resonator. and providedwith arr aperture coincident with the-aperture of said wall portion ofsaid primaryj resonatorA and a second wall portion provided with an'aperture in linewith the apertures in said. contiguouswall' fportiruas,and a 'secondsecondari cavity resonator; having a wall portioncontiguous4 to the other orsaidwailpprtionsonsaid.primary resonatorancifprovidedwith an aperture coincident with the aperture of said otherof said Wall portions of said primary resonator and a second wallportion provided with an aperture in line with the apertures in saidsecond contiguous Wall portions, said rst and said second secondaryresonators having a resonant frequency corresponding to the resonantfrequency of said primary resonator.

5. A cavity resonator system comprising a primary cavity resonatorhaving spaced wall portions each provided with an aperture having adiameter which is small with respect to the spacing between said wallportions, and two secondary cavity resonators each positioned adjacentto one of said wall portions, said secondary resonators each having arst wall portion contiguous to said wall portions of said primaryresonator and provided with an aperture coincident with said aperture ofsaid contiguous wall portion and a second wall portion provided with anaperture in line with said apertures of said contiguous wall portions,each of said secondary resonators having a resonant frequencycorresponding to the resonant frequency of said primary resonator.

6. A cavity resonator system comprising a primary cavity resonatorhaving spaced wall portions each provided with an aperture having adiameter which is small with respect to the spacing between said wallportions, and two secondary cavity resonators each positioned adjacentto one of said wall portions, said secondary resonators each having airst wall portion contiguous to said wall portions of said primaryresonator and provided with an aperture'coincident with said aperture ofsaid contiguous wall portions and a second wall portion comprising atubular member extending within said second secondary resonator, saidtubular member being provided with a bore an axis of which is coincidentwith the axis of the apertures of said contiguous wall portions, andsaid secondary resonators having a resonant frequency corresponding tothe resonant frequency of said primary resonator.

7. A cavity resonator system comprising a primary cavity resonatorhaving spaced wall portions each provided with an aperture having adiameter which is small with respect to the spacing between said wallportions, and two secondary cavity resonators each positioned adjacentto one of said wall portions each of said secondary resonators having afirst wall portion contiguous to one of said wall portions of saidprimary resonator and provided with an aperture coincident With saidaperture of said contiguous Wall portions and a second wall portion,said second wall portion comprising a tubular member extending withinsaid second secondary resonator to an antinode potential region andprovided with a bore an axis of which is coincident with the axis of theapertures of said contiguous wall portions, said secondary resonatorshaving a resonant frequency corresponding to the resonant frequency ofsaid primary resonator.

8. A cavity resonator system comprising a primary cavity resonatorhaving spaced wall portions each provided with an aperture having adiameter which is small with respect to the spacing between said wallportions, and two secondary cavity resonators each having a wall portionincluding said aperture in common with said primary resonator, each ofsaid secondary resonators comprising two concentric conductors the axesof which are coincident with the axis of said apertures of said commonwall portions, and means interconnecting said conductors at the endsthereof remote from saidy common wall por-l tions said secondaryresonators having a resonant frequency corresponding to the resonantfrequency of said primary resonator.

9. A cavity resonator system comprising a primary cavity resonatorhaving spaced wall portions each provided with an aperture having adiameter which is small with respect to the spacing between said Wallportions, and two second--v ary cavity resonators each having a wallportion including said aperture in common with said resonator, each ofsaid secondary resonators comprising two concentric conductors, the axesof which are coincident with the' axis of said apertures of said commonwall portions, and means interconnecting said conductors at the endsthereof remote from said common wall portions, the inner conductor ofsaid conductors ter-z minating at an antinode potential region in thesecondary resonator, said secondary resonators having a resonantfrequency corresponding to. the resonant frequency of said. primaryresonator.

10. A cavity resonator system comprising a primary resonator havingspaced wall portions each provided with an aperture having a diameterwhich is small with respect tothe spacing between said wall portions,and two secondary cavity resonators each having a wall portion includingsaid aperture in common with said primary resonator, each of saidsecondary resonators comprising two concentric cylindrical conductorsthe axes of which are coincident with the axis of said apertures of saidcommon wall portions, and a `disc member interconnectingv saidconductors at the ends thereof remote from the common wall portion, saidsecondary reso'- nators having a resonant frequency corresponding to theresonant frequency of said primary resonator.

11. A cavity resonator system comprising a rst group of cavity resonatorelements, a second group of cavity resonator elements spaced from andaxially aligned with said rst group, each of said groups comprisingprimary cavity resonator having spaced wall portions each provided withan aperture, and a first secondary cavity resonator each having a wallportion including said aperture in common with said primary resonatorand comprising two concentric tubular conductors the axes of each arecoincident with an axis of said aperture of said common Wall portionsand means interconnecting said conductors at the ends thereof remotefrom said common wall portions, said first group of cavity resonatorsfurther comprising a concentrator solenoid positioned adjacent to saidprimary resonator, and a second secondary cavity resonator comprising awall portion positioned adjacent to said solenoid and provided with anaperture axially aligned with the apertures of 60 the primary cavityresonator, said second secondary resonator further comprising twoconcentric tubular conductors the axes of which are coincident with theaxis of said apertures of said common wall portions and meansinterconnecting 65 said conductors at the ends thereof remote from saidcommon wall portions, a tubular conducting member interposed betweensaid primary resonator and said second secondary resonator and throughsaid solenoid said second group of cavity 7o resonators comprising asecond secondary cavity resonator comprising two concentric tubularconductors the axes of which are coincident with the axis of saidaperture of said common wall portions and means interconnecting saidconductors 75 at the ends thereof remote from said common andere wallportions; theinner conductor of saidisecondary Ycavity resonators4extending within the resonator to anantinode potential region, meanselectrically coupling the'primary cavity resonators of each of saidgroups,the resonant frequency of the resonator of said first groupcorresponding to the resonant frequency of the resonator of said secondgroup, and the resonant frequency of said secondary resonatorsof each ofsaid groups corresponding to the resonant frequency of the primaryresonator of said groups.

12. A cavity resonator .system comprising a first group of cavityresonator elements, a second group of cavity resonator elements spacedfrom and axially aligned with said rst group, each of said groupscomprising primary cavity resonator having spaced wall portions eachprovided with an aperture and a rst Secondary cavity resonator eachhaving a wall portion including said aperture in common with saidprimary resonator and comprising two concentric tubular conductors theaxes of each are coincident with the axis of said aperture of saidcommon wall portions and means interconnecting said conductors at theends thereof remote from said common wall portions, said rst group ofcavity resonators further comprising a concentrator solenoid positionedadjacent to said primary resonator, and a second secondary cavityresonator comprising a wall portion positioned adjacent to said solenoidand provided with an aperture axially aligned with the apertures of theprimary cavity resonator, said second secondary resonator furthercomprising two concentric tubular conductors the axes of which arecoincident with the-axis of said apertures of said common wall portionsand means interconnecting said conductors at the ends thereof remotefrom said common wall portions, a tubular conducting member interposedbetween said primary resonator andsaid second secondary resonatorandthrough said solenoid, said second group of cavity resonators comprisinga second secondary cavityresonator comprising two concentric tubularconductors the axes of which are coincident with the axis of saidaperture of said common wall portions and means interconnecting saidconductors at the ends thereof remote from said common Wall portions,the inner con-` ductor of said secondary cavity resonators extendingwithin the resonator to an antinode potential region, means electricallycoupling the primary cavity resonators of each of said groups, theresonant frequency of the resonator of said iirst group corresponding tothe resonant frequency of the resonator ofsaid second group, theresonant frequency of said secondary resonators of each of said groupscorresponding to the resonant frequency of the primary resonator of saidgroups, means to generate an electron beam axially aligned with andarranged on the side of said first group of cavity resonator elementsremote from said concentrator solenoid, focusing means interposedbetween said generator means and said side of said rst group to trajectsaid beam into the apertures of said groups of cavity resonator elementsand means to collect electrons from said beam axially aligned and:arranged at the end of said groups remote from said generator means.

FREDERIK COETERIER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,242,275 Varian May 20, 19412,263,648 Salzberg Nov. 25, 1941 2,280,824 Hansen et a1 Apr. 28, 19422,323,729 Ryan July 6, 1943 2,391,016 Ginzton et al Dec. 18, 19452,403,795 Hahn July 9, 1946 2,409,179 Anderson Oct. 15, 1946

